1. Field of the Invention
The present invention relates to a method for making reinforcing structures for vehicle tyres, comprising the step of laying down at least one continuous thread-like element onto a support element, according to a deposition path substantially concentric with the rotation axis of the tyre.
The invention also relates to a tyre integrating reinforcing structures made according to said method, said tyre being of the type comprising a carcass structure including at least one carcass ply having its ends in engagement with respective circumferentially inextensible annular anchoring structures; said carcass ply having two axially-opposite side portions separated from each other by a crown portion and each extending radially away from one of the annular anchoring structures until said crown portion; a belt structure applied to said crown portion at a radially external position relative to the carcass ply; a pair of sidewalls applied to said side portions at an axially external position relative to the surfaces of the carcass ply; a tread band applied to the belt structure at a radially external position thereof; reinforcing structures, each comprising at least one continuous thread-like element extending in an undulated trajectory substantially concentric with the rotation axis of the tyre.
2. Description of the Related Art
Manufacture of tyres for vehicle wheels involves formation of a carcass structure essentially made up of one or more carcass plies shaped in a substantially toroidal configuration and having their axially opposite side edges in engagement with respective annular anchoring structures integrating circumferentially inextensible annular inserts usually referred to as “bead rings” placed at the tyre regions usually identified with the name of “beads”.
Applied to the carcass structure, at a radially external position, is a belt structure comprising one or more belt layers in the form of a closed loop, substantially made up of textile or metallic cords suitably oriented with respect to each other and to the cords belonging to the adjacent carcass plies.
At a radially external position to the belt structure a tread band is applied usually comprising a strip of elastomeric material of appropriate thickness.
It should be pointed out that, to the aims of the present description, by the term “elastomeric material” it is intended blends of rubber in their entirety, i.e. assemblies formed of at least one base polymer suitably amalgamated with reinforcing fillers and process additives of various types.
Finally, to the opposite sides of the tyre being processed, a pair of sidewalls is applied each of which covers a side portion of the tyre included between a so-called shoulder region, located close to the respective side edge of the tread band, and a so-called bead located at the corresponding bead-ring.
Tyres are generally classified into at least two categories, differentiated from each other due to the orientation exhibited by the cords being part of the carcass plies. In particular, there are the so-called “radial tyres” in which each of the cords arranged in the carcass ply or plies lies in a plane substantially radial to the rotation axis of the tyre, i.e. has an orientation substantially orthogonal to the circumferential extension direction. Then there are the so-called tyres “of the conventional type” or “cross-ply tyres”, the carcass structure of which generally comprises at least one carcass ply having cords oriented obliquely to the circumferential extension direction of the tyre, and a second carcass ply, radially superposed on said first ply, the cords of which exhibit a symmetrically-crossed oblique orientation with respect to the cords of the first ply.
Tyres of the radial type, as compared with those of the conventional type, offer advantages in terms of lightness, ride comfort, resistance to wear and structural strength to high speeds. Conversely, they have a sidewall of weaker structure than tyres of the conventional type, so that a possible failure at the sidewall usually involves the tyre being out of use.
The above features have caused the tyres of the conventional type to be basically fallen into disuse in those Countries where a modern road network (minimising the risk of accidental failures to the sidewall) is present, in favour of tyres of the radial type.
Development in time of these tyres has led to a progressive reduction in their section height also for the purpose of obviating the feeling of ride unsteadiness generated by the sidewalls that are radially very extended.
In particular cases and/or for specific uses requiring that the tyre sidewalls should have a higher strength than that offered by the carcass ply, also in combination with a reduced section height, the sidewalls of a tyre is to be strengthened by means of additional reinforcing elements.
In particular, from document U.S. Pat. No. 3,044,522 reinforcement for tyres is known which is assembled on a collapsible drum and subsequently applied to the tyre carcass. The reinforcement is made up of layers axially disposed in a side-by-side relationship upon interposition of an elastomeric filling element. Each layer is defined by a plurality of coils disposed radially in side-by-side relationship and extending in a sinuous course having predetermined pitch and width. In addition, the coils of two distinct layers are circumferentially offset relative to each other, by about half a pitch.
Document U.S. Pat. No. 3,044,522 in the same manner as many other traditional production methods, essentially involves that the individual tyre components should be first made separately from each other to be then assembled during a tyre-building step.
The Applicant's present trend is however that of resorting to manufacture methodologies enabling production and storage of semi-finished articles to be minimised or, if possible, eliminated.
Practically, the research and development studies carried out by the Applicant are oriented to new process solutions allowing the individual components to be made by directly forming them on the tyre being built, preferably following a pre-established sequence.
This is particularly suitable above all in the production of tyres of the radial type.
In this connection, production processes have been proposed which aim at obtaining given tyre components, such, for example, as tread band, sidewalls or others, by laying down onto a toroidal support carrying the tyre being worked, a continuous strip-like element of elastomeric material having a reduced section as compared with that of the component to be obtained and disposed to form a plurality of coils around the rotation axis of the tyre, which coils are arranged consecutively in side by side relationship and/or superposed on each other so as to define the component itself in its final configuration.
In the European Patent Application No. 01830350.3 the Applicant has proposed adoption of annular stiffening inserts placed at the sidewalls of the radial tyres to increase stiffness of same, obtained by circumferentially winding at least one continuous thread-like element into several consecutive turns so as to form a series of coils disposed in radial side by side relationship and concentric with the geometric rotation axis of the tyre.
The Applicant has perceived that, notwithstanding the good results achieved with these inserts formed of one or more spiral-wound thread-like elements, there is still an interest in trying to improve tyre performance, in particular as regards increase in the sidewall stiffness of tyres intended for equipping two-wheeled vehicles. In fact, during the ride on a bend these tyres bank with respect to the vertical, according to camber angles of a very high value, thereby submitting the tyre sidewalls to important stresses.
These tyres have a marked transverse curvature at the crown which is normally defined by the particular value of the ratio between the distance of the tread centre from the line passing through the laterally opposite extremities of the tread itself, measured at the equatorial plane of the tyre, and the distance measured along the tyre chord between said extremities. In tyres for two-wheeled vehicles the value of the curvature ratio is generally at least about 0.15 and usually it is of about 0.3 in the case of rear tyres and also higher, until about 0.45, in the case of front tyres, versus a value usually of about 0.05 in motor-vehicle tyres.